1. Field of the Invention
This invention relates to an abrasive tape which is used to polish a magnetic head or the like. This invention particularly relates to an abrasive tape which is used for finish polishing of a rough-polished surface of a magnetic head or the like.
2. Description of the Prior Art
Video or high-grade audio magnetic heads are made by being polished with abrasive tapes. The abrasive tape comprises a flexible substrate, and an abrasive layer overlaid on the flexible substrate. In order to provide the abrasive layer, an abrasive coating composition consisting of abrasive grains, a binder, additives and the like is applied onto the flexible substrate and dried.
The term "abrasive tape" as used herein broadly embraces abrasive members which take on the form of a long strip or a disk. In general, when the surface of a magnetic head or the like is to be polished with a long strip-like abrasive tape, two reels are positioned with the magnetic head or the like intervening therebetween, and the abrasive tape is moved in contact with the surface to be polished between two reels. In cases where a disk-shaped abrasive tape is used, the disk is rotated in order to polish a surface.
The abrasive tape is flexible and can snugly fit to a curved surface. Therefore, the abrasive tape is more suitable for the polishing of the curved surface of the magnetic head or the like than grinding wheels. Also, the abrasive tape can achieve scratch-free, accurate polishing of the surface to be polished, and is therefore indispensable to finish polishing of a rough-polished surface.
In cases where the abrasive tape is moved in an polishing apparatus in order to polish a surface of a magnetic head, it is necessary that movement stability of the abrasive tape be kept good. Also, the surface of the abrasive tape should be prevented from being electrostatically charged. Furthermore, abrasive grains should be dispersed uniformly in an abrasive layer of the abrasive tape. Specifically, if movement stability of the abrasive tape is low, the abrasive tape will stick and slip on the surface of the magnetic head and generate a chirping sound during movement. In such cases, the surface to be polished cannot be polished uniformly. If the surface of the abrasive tape is electrostatically charged due to friction with the surface to be polished, ambient dust will stick to the surface of the abrasive tape and will undesirably scratch the surface to be polished. If abrasive grains are dispersed nonuniformly in the abrasive layer of the abrasive tape, the abrasive grains will agglomerate locally and will undesirably scratch the surface to be polished.
Various methods have been proposed in order to solve the problems described above. For example, in Japanese Patent Publication No. 62(1987)-37447, a method is proposed wherein additives such as a lubricant and an antistatic agent are added to an abrasive layer of an abrasive tape, and the proportions of the additives are changed in order to adjust the coefficient of friction of the surface of the abrasive tape. In U.S. Pat. No. 4,764,423, a method is proposed wherein a fatty acid, a fatty acid ester, silicone oil, and a surface-active agent are added to an abrasive layer of an abrasive tape in order to improve movement stability of the abrasive tape. Also, in Japanese Unexamined Patent Publication No. 61(1986)-265279, a method is proposed wherein a dispersing agent and an antistatic agent, such as carbon black or titanium black, are added to an abrasive tape.
However, with the proposed methods, the lubricant, the antistatic agent, and the dispersing agent are added independently in order to improve tape movement stability, to prevent electrostatic charging, and to improve dispersibility of abrasive grains. Therefore, when these additives are added to the abrasive layer of the abrasive tape so that all of the three requirements are satisfied, the proportions of the additives to the abrasive layer increase. As a result, strength of the abrasive layer deteriorates, and polishing performance of the abrasive tape becomes bad.